Akinori Maeda

Luminescence of dyes doped in a sol–gel coating film

Abstract A sol–gel coating film doped with coumarin 6 as a host and rhodamine 6G as a guest was prepared by a sol–gel technique. A coumarin 6-doped sol–gel coating film showed the spectral changes of absorption and fluorescence due to the change of molecular structure originating from the acid–base equilibrium of immobilized dyes. A rhodamine 6G-doped sol–gel coating film did not show these spectral changes. However, when rhodamine 6G was doped together with coumarin 6 in a sol–gel coating film, its emission showed increase in intensity with the increase of pH, irrespective of a constant absorption of irradiated photons. Based on these observations, energy transfer between coumarin 6 and rhodamine 6G was examined.

Thermally Stimulated Currents in Polyethylene Terephthalate due to Injected Charge

Thermally stimulated currents (TSC) from polyethylene terephthalate (PET) electrets have been investigated in the temperature range from -190 to +120°C. PET electrets were formed by applying a high field in a short time at various temperatures. Both dependencies of TSC on electrode metals (Au, Al) and the polarity of an applied field were remarkable in the temperature range above -40°C. The results indicate that electrons injected from the Al cathode greatly contribute to the TSC above -40°C and that the TSCs below -40°C for Al electrodes and at all temperatures for Au electrodes are mainly induced by the depolarization of dipoles.

Optical pH sensing characteristics in dye-doped sol-gel coating film based on the energy transfer

Optical pH sensing characteristics based on the energy transfer using the sol–gel coating film doped with coumarin 6 and rhodamine 6G were examined. The dynamic range was a wider pH region from 1.0 to 10.0 and an optimum molar ratio of the two dyes existed from the viewpoint of the highest sensitivity for all pH levels. The response time for pH change from 1.0 to 10.0 was faster than that from pH 10.0 to pH 1.0. At a low HCl concentration as a catalyst, response times were constant under some molar ratio of the two dyes and agreed with that of coumarin 6-doped sol–gel coating film. At a high HCl concentration as a catalyst, response times which depend on the pore size in the silica network were long and constant, irrespective of the molar ratio of the two dyes. These characteristics were not significantly affected by the passage of days.

Thermally Stimulated Current in Polyethylene Terephthalate Electrets Formed by AC Electrical Fields

Thermally stimulated current (TSC) in polyethylene terephthalate (Au-PET-Al) was investigated with excitation by AC electric field. Two TSC peaks were observed above room temperature and were ascribed to the release of trapped electrons injected from the Al electrode. This TSC analysis with AC electric field excitation can easily evaluate the peak of trapped electronic carriers separating from other peak due to dipolar polarization.

Coumarin-4-Doped Sol-Gel Coating Film as Optical pH Sensor

Coumarin 4, a pH indicator, was entrapped in a silica matrix coated as a thin film onto a silica substrate by the sol-gel technique. The absorbance and fluorescence changes of the immobilized indicator were examined in the pH sensing range. The increase in absorption and fluorescence intensities as the acid form of the immobilized coumarin 4 is converted to its basic form, is dependent on pH. The dynamic range and the response time of this probe were pH 3-9 and less than 10 s, respectively.

Humidity Dependence of Photoluminescence in Coumarin-4-Doped Sol-Gel Coating Film

Coumarin 4 dye was doped in a silica matrix coated as a thin film by means of the sol-gel technique. The fluorescence intensity of the immobilized dye was quenched by moisture. The humidity dependence of the fluorescence intensity was examined in the relative humidity range between about 3 and 90% as a function of the concentration of coumarin 4 and catalytic aqueous HCl. The obtained results reveal that the fluorescences emitted from both the coumarin 4 monomer and the aggregates of dye molecules are quenched by moisture and their quenching is explained by the Stern-Volmer equation.

Photophysics of coumarin 4 doped-amorphous silica glasses prepared by the sol-gel method

Abstract Fluorescence and absorption spectra and fluorescence decay curves of coumarin 4 doped-amorphous silica glasses prepared by the sol-gel method were studied. With increasing acidity of hydrolysis, the peaks of the first absorption band and the corresponding fluorescence spectra show abrupt red-shift around 0.1 N HCl concentration. Another two emission bands appear at 470 and 500 nm. The former band is independent of the HCl concentration less than 0.1 N , while with increasing HCl concentration more than 0.1 N these emission intensities increase. These results are related with the molecular forms of coumarin 4.

Electrical conduction and electroluminescence of vacuum-evaporated thin TCNQ films

Electroluminescence (EL) and electrical conduction in TCNQ (tetracyanoquinodimethane) thin films prepared by the vacuum-evaporation technique were investigated. X-ray diffraction studies showed that the specimen prepared at 280 degrees C was crystalline, while the one prepared at 180 degrees C was amorphous. An infrared (IR) absorption analysis showed that the main chemical composition of TCNQ has been largely preserved in the vacuum-evaporated films. The polarized IR spectrum indicated that the aromatic ring of the evaporated TCNQ molecules is arranged nearly parallel to the substrate. The electrical properties depended strongly on the film deposition conditions, such as deposition rate and/or temperature and substrate temperature. The conduction currents were also affected by the electrode materials. Higher conductivity was observed in the specimen with a Cu anode than that with Au or Al. A weak EL which was well in proportion to the conduction current was observed in the high-field region of >10/sup 5/ V/cm. The thermally stimulated current showed two peaks at -120 and -20 degrees C. The trap depths were estimated as 0.10 and 0.22 eV, respectively. >

pH Dependence of Luminescence in Dye-Doped Sol-Gel Coating Film

A rhodamine 6 G-doped sol-gel coating film did not show spectral or intensity changes in absorption or fluorescence in the acid-base equilibrium of immobilized dyes. When rhodamine 6 G was doped together with coumarin 6 and fluorescein in sol-gel coating films, its emission showed an increase in intensity with the increase of pH. These observations were related to energy transfer from coumarin 6 and fluorescein to rhodamine 6 G. The sensitivity region of this emission intensity to pH change was improved by using a two dye-doped sol-gel coating film.

Optical pH Sensing Properties of Coumarin-4-Doped Sol–Gel Coating Film

Immobilized coumarin-4 coating film prepared by the sol–gel process was used as an optic pH sensing probe. The coumarin dye shows emission bands around 430 and 395 nm appearing in the acid-base reaction of coumarin 4. The probe response relies on the change of the fluorescence intensity ratio under emission bands at 430 and 395 nm. That stability is examined and related with the preparation conditions of the sol–gel coating films.